/Engine/Plugins/MovieScene/MovieRenderPipeline/Source/MovieRenderPipelineCore/Public/Graph/Nodes/MovieGraphRenderPassNode.h
Called each output frame. Should add a series of FMovieGraphRenderDataIdentifiers to the array, and then when producing frames in Render, the resulting image data should have the matching FMovieGraphRenderDataIdentifiers associated with it. Used by the Output Merger to ensure all of the render data for a given frame has been generated before passing it on to write to disk. Called on the CDO.
void GatherOutputPasses ( [TArray](API\Runtime\Core\Containers\TArray)< [FMovieGraphRenderDataIdentifier](API\Plugins\MovieRenderPipelineCore\Graph\FMovieGraphRenderDataIdentifier) > & OutExpectedPasses ) const